Television equipment



NOV. 26, 1935. B, F, LOFG EN 2,022,248

TELEVIS I ON EQUIPMENT Fil'ed March 10, 1950 cell longer than PatentedNov. 26, 1935 TES 2,022,248 TELEVISION EQUIPMENT Benjamin F. Loigren,

American Telephone and Sandy, Utah, assignor to Telegraph Company,

New York, N. Y., a corporation of New York Application March 21 Claims.

This invention pertains to the art of transmitting pictures electricallyand especially to television. The principal object of this invention is:means to analyze an object or an image as to light values and theproduction of corresponding electric values.

As is generally known the usual analysis of a picture for televtision isaccomplished by passing a small aperture across 'an image of the picturein adjacent lines so that the light from small areas of the image passin turn into a photoelectric cell to vary the resistance in an electriccircuit, thus producing electric values proportionate to the lightvalues of the picture. Other systems cause the image to move and theaperture to remain stationary; but all present systems analyze thepicture by taking the light from fractional areas in turn of the imageor picture. Thus the light values being used at any time is the sum ofthe light of all the points in that fractional area. Evidently thismethod can not respond to the fine points or lines of a picture and thereproduced picture will consequently be vague or difiused.

The present invention purposes to largely eliminate that effect byanalyzing in a new manner hereinafter described.

The systems now known for analyzing a picture use the light from eachsmall fractional area during its proportionate time only, to operate thephoto-electric cell. And since the photo-electric circuit producesrelatively small currents the electric values obtained are extremelysmall, necessitating great amplification. The present invention purposesto analyze the picture by a method which allows the light from each partof the picture to operate the photo-electric its proportionate time anduses the accumulated light effect to produce instantaneous electricvariations. 1

With these and other purposes and objects in view this inventionconsists in the novel apparatus and methods hereinafter described andparticularly pointed out in the claims.

Fig. I is an illustration of the general scheme showing the analyzingapparatus.

Fig. II shows more in detail the image being analyzed where twophoto-electric circuits are used.

Fig. III shows in detail the image being analyzed where threephoto-electric circuits are used.

Fig. IV illustrates the electrical results ob tained when using theusual method of analyz- 10, 1930, Serial No. 434.,6fl0

ing as compared with the results when using the invention hereindescribed.

Referring to the drawing and especially to Fig. I, the lens L focuseslight from an object P to form an image a-ng-h on a rotatable 5 drum l.The drum l contains a series of slits Si, S2, S3, etc. arranged in abroken spiral form of one turn, so that as the drum rotates the slitspass through the image in different lines. When a slit is in the imagethe light from a narrow my strip of the image passes through the slit.Two or more photo-electric cells 2, 3, (ID) are placed to receive thelight which passes from the image through the slits, each cell receivingfrom its proportionate part of the image area. For the pur- 5 pose ofmore accurately dividing the image area into sections a divider 9 (ordividers 9, 9 Fig. III) is placed between the photo-electric cells sothat the light from any one point in the image will fall into only onecell. Each photo- 29 electric cell is connected in an electrical circuitwith a proper electromotive force and an inductance coil. Cell 2 is incircuit with a potential 3 and an inductance 4, while cell 3 is incircuit with a potential 8 and an inductance 5, so that 5 any lightwhich passes into a cell causes a proportionate current to flow throughthat particular circuit.

The slits are so arranged that the distance from one to the next isequal to the width of one 30 section or division of the image, that is,the width of image which operates one cell.

Fig. II shows more clearly the relationship between the slits, image andcells where two cells are used. The distance between slits equals one 35half the image width and the length of the slits is minutely longer. Itis readily seen that light can enter a cell through only one slit at anytime. When any part of a slit is between the divider 9 and a-h the lightfrom that part or the image 40 passes into cell 3 and when any part of aslit is between the divider 9 and n-g the light from that part of theimage passes into cell 2. As the drum I rotates each slit in turn admitsthe light from a narrow strip of each half image 45 into its particularcell and then cuts the light out. But always while a slit is cuttinglight into one cell it, or another slit, is cutting light out of theother cell. The two cases are illustrated in Fig. II. At the top of theimage S! is cutting 50 light into cell 3 and at the same time, iscutting light out of cell 2. As soon as S! is out of the cell 2 halfimage S2 will begin to enter. In another case, shown at the bottom ofthe image, one slit, say S30 is cutting light out of cell 3 55 while S3!is cutting light into cell 2. part of the image in turn is cut into acell and then cut out. But this increasing or decreasing light flux in acell causes a proportionate increase or decrease in the electric currentin that particular circuit. In the circuit with each photo-e1ectric cellis an inductance coil so that any current in the circuit produces amagnetic field about the inductance coil and any change in currentproduces an electromotive force or potential across the coil; when thecurrent is decreasing the potential is in one direction and when thecurrent is increasing the potential is in the opposite direction. Eachinductance coil is connected in another circuit containing a rectifyingvalve 6, l and in common a vacuum tube l3. These rectifying valves areso connected that only the coil in which the current is decreasing canpass its induced electromotive force to control the tube 53. Since theslits are cutting light out of only one cell at any time only one cellat a time has its force in the right direction to operate tube 53. Thustube is is controlled at any instant by the potential across aninductance coil, which potential is proportional to the rate of decreaseof current in that coil, which is proportional to the rate of decreaseof light flux in that photo-electric cell, which is proportional to thelight intensity at that particular spot in the image being cut out.

In the event that such high inductance coils are used that there is aconsiderable lag in the Thus each growth of the current where the lightis increas-- ing or in the event that such sensitive photo-electriocells are used that a wide variation in light flux entering isundesirable then more than two cells, with their dividers and electriccircuits, can be used. In such a case there is a longer time after thecutting of light into a cell before the cutting out begins; in whichtime the current can become established thus accumulating the lighteffect in the circuit. At the cutting out of light there is no lag inthe drop of current and a relatively high potential is obtained by anelectromagnetic action in the coil similar to an induction coil at breakof circuit.

Fig. III illustrates the arrangement for three photo-electric cells withtheir corresponding circuits. The distance between slits is equal to thewidth of one division of the image and the length of the slits equalsthe width of the image less one division.

When the image of a moving object is to be analyzed, such as a movingpicture film or an object viewed from a moving airplane then the slitswill be arranged to pass through the subject matter of the image indifferent lines. The positions of the slits on the rotating drum willdepend upon the relative velocities of the slit and the moving obiect.However, one skilled in the art can properly arrange the slits to meetthat situation, keeping in mind that the entire length of a slit mustpass through the same line in the subject matter of the image.

A disc or belt containing slits might be used in place of the drum, butthat would not require invention. Modifications in construction might bemade without changing the principles of this invention. For example, acompound photoelectric cell might be used in place of a number of singlecells and might also incorporate the dividers. The slits might be usedin more than one turn on the drum by introducing suitable shutters or aswitching device to connect only the desired numberof cells at a time;or the slitsmight be in a stationary diaphragm and the image move,provided always that only one cell having one slit cutting light out,can operate Vacuum tube l3 at any time. Larger openings might let lightinto a cell but a small cutting member cut the light out in narrowstrips in turn. Yet all these variations in detail are within theprinciples of this invention.

One of the advantages of this invention over the usual analyzing deviceis illustrated in Fig.

IV. A black line l5 in the image being analyzed is shown being crossedby the slit S as in this invention and by a hole H as in the usualmethod. As the slit S moves, the black line has no influence on the rateof cutting out light last end meets the black line. Instantly the rateof cutting drops to zero until the black line is passed, then the rateof cutting instantly is up proportional to the intensity of the light.Since the potential Vs is proportional to the rate of cutting out oflight it follows the light intensity very closely. With the usual hole Hpassing the black line the resultant current Il-I falls gradually, doesnot quite reach zero then rises gradually, thus producing a fading ordifiusing eiiect.

Another advantage of the present invention lies in the fact that anincrease in the number of lines into which the image is cut will notreduce the potential values developed, since all the light must be cutin and then out once over the pic- But with the hole disc the resultantcurrent depends on the area of the hole which is greatly reduced byincreasing the number of holes.

This invention uses the light from each point of the image for a longertime than its proportionate time and accumulates the effect in amagnetic field about an inductance coil and the resultant is taken as aninstantaneous potential as the light is cut out.

Thus the light intensities of infinitely small parts of the image, takenin turn, produce a correspondingly varying potential which controls tubeI3. The current from this tube is amplified for transmission to areceiving station for picture reproduction or is used as a measure ofthe light values of the analyzed object.

Although a device pertaining to picture transmission is given as theprincipal object of this invention, yet there are elements in thisinvention which are useful for other purposes, such as photometry andcolor analysis.

Having described my invention, what I claim is:

l. The method of electro-optical scanning which comprises progressivelyand continuously varying the size of the region of a picture field fromwhichlight is utilized throughout the scanning operation, and utilizingthe rate of change of size of said region to control the production ofan electromotive force which continuously corresponds to the rate ofchange of light from said region.

2. Scanning apparatus comprising light sensitive electric means forreceiving light modified by a picture field of View, and means fordetermining the region of said field from which light is at any instantreceived by said light sensitive means and for causing a progressivecontinuous change in the size of said region as the scanning proceedsthroughout the complete scanning period.

3. Scanning apparatus comprising light sensitive electric means forreceiving light. modified by a picturefield of view, and means fordeteruntil the 2,022,248 mining the region of said field from whichlight is received by said light sensitive means at each instant and forprogressively and continuously varying the size of said region fromwhich light is received by varying a portion only of the boundary ofsaid region throughout the complete scanning period.

4. Television scanning apparatus comprising light sensitive electricmeans for receiving light modified by a picture field of view androtatable apertured scanning means for determining the region of thefield from which light is received by said light sensitive means and forprogressively continuously varying the size of said region as thescanning proceeds throughout the complete scanning period.

5. Scanning apparatus comprising light sensitive electric means forreceiving scanning light from a picture field of view, and meansincluding a rotatable scanning element having rectangular shaped slotstherein for respectively determining in succession regions of the fieldfrom which light is received by said light sensitive means and forprogressively continuously causing the size of each of said regions todecrease from a maximum value to zero as the scanning proceedsthroughout the complete scanning period. c

6. In a scanning system, an electrical light sensitive device forreceiving light rays from all points of a picture field of view and onlyfrom said field, scanning means for determining the region of the fieldfrom which the light is effective on said device at any given instant,means for changing the area of said region in a predeterminedprogressive continuous manner as the scanning proceeds throughout thecomplete scanning period, an inductance coil connected in series withsaid light sensitive device, and means to utilize the voltage generatedacross at least a portion of said coil.

'7. Scanning apparatus comprising light sensitive electric means forreceiving scanning light from a picture field of view, means to confinethe light from one portion of the field to one portion of said lightsensitive means andthe light from another portion of the field to asecond distinct portion of said light sensitive means, means fordetermining the regions ofeach of the portions of said field from whichlight is at any instant received by both portions of said lightsensitive means and causing a progressive continuous change in the sizeof the said regions as the scanning proceeds throughout the completescanning period and means for transmitting effective image currentscontrolled by only a single portion of said light sensitive means at anygiven time.

8. Scanning apparatus comprising a light sensitive electric means forreceiving light from a field of view and only from said field, a movablescanning means having a plurality of elongated apertures for exposing tosaid light sensitive device entire elemental lines of said fieldsuccessively upon movement thereof, the apertures being so arranged thatlight from only a single line is incident upon said light sensitivedevice at any given instant, means to move said scanning means tosuccessively expose said elemental lines, and means for utilizing thecurrent produced in the light sensitive device to control the productionof image currents only when the effective area of an exposed elementalline is progressively changing in a single direction.

9. Scanning apparatus comprising means to form an image of an object tobe scanned, a rotating scanning drum coincident in part with said image,elongated apertures in said drum of elemental line width and length atleast equal to the length of an elemental line of said image, saidapertures being arranged to scan elemental lines successively and beingseparated end to end by at least the length of an elemental line, alight sensitive electric device for receiving light from said imagethrough said apertures, and means for utilizing the current produced inthe light sensitive device to control the production of image currentsonly when corresponding ends of the apertures lie within the image area.being scanned.

10. Scanning apparatus comprising a scanning drum, a plurality ofelongated apertures arranged around the surface of'said drum separatedend to end by a distance equal to the length of an aperture and off-setacross the drum so as to trace at least partially distinct paths as thedrum rotates, a light sensitive electric device adapted to be energizedby light incident thereon through a single aperture at any giveninstant, and means for utilizing the current produced in the lightsensitive device to control the production of image currents only whenthe effective size of any aperture is progressively changing in the samedirection due to rotation of the drum.

11. Scanning apparatus comprising a scanning drum, a plurality ofelongated apertures arranged around the surface of said drum separatedend to end by a distance equal to the length of an aperture and off-setacross the drum so as to trace at least partially distinct paths as thedrum rotates, a light sensitive electric device adapted to be energizedby light incident thereon through a single aperture at any giveninstant, and means for utilizing the current produced in the lightsensitive device to control the production of image currents only whenthe effective size of any aperture is progressively decreasing due torotation of the drum.

12. Scanning apparatus comprising a scanning drum, means for rendering alimited area of said drum surface effective for scanning at any giveninstant, a. plurality of light sensitive electric de vices adjacentdistinct portions of said limited area, a plurality of elongatedapertures arranged around said drum in such a manner as to scandifferent elemental lines of said area, the length of said aperturesbeing at least equal to the width of said area less the width of thenarrowest distinct portion and the separation between apertures end toend being at least equal to the width of the widest distinct portion,and means for utilizing, to control the production of image currents,the current produced only in that light sensitive device correspondingto the distinct portion across which corresponding ends of the aperturesare moving to progressively change the effective area in the samedirection due to rotation of the drum.

13. Scanning apparatus comprising a scanning drum, means for rendering alimited area of said drum surface effective for scanning at any giveninstant, two light sensitive electric devices each adjacent to one-halfof said limited area measured around the drum, a plurality of elongatedapertures arranged around said drum in such a manner as to scandifferent elemental lines of said area, the length of each of saidapertures as well as the separation between said aperture end to endbeing at least equal to one-half the width of said limited area, andmeans for utilizing, to control the production of image currents, thecurrent produced only in that light sensitive device corresponding tothat half of said limited area wherein the size of the aperture isprogressively decreasing due to rotation of the drum.

14. Scanning apparatus comprising a scanning drum, means for rendering alimited area of said drum surface efiective for scanning at any giveninstant, three light sensitive electric devices each adjacent toone-third of said limited area measured around the drum, a plurality ofelongated apertures arranged around said drum in such a manner as toscan different elemental lines of said area, the length of each of saidapertures being at least equal to two-thirds the width of said limitedarea and the separation between apertures end to end being at leastequal to onethird the width of said limited area, and means forutilizing, to control the production of image currents, the currentproduced only in that light sensitive device corresponding to that thirdof said limited area wherein the size of the aperture is progressivelydecreasing due to rotation of the drum.

15. The method of scanning which comprises dividing the light from apicture field of view into successive regions, each having a maximumarea corresponding to an extended portion of the field, utilizing thelight from each region to control the production of an electromotiveforce, and progressively continuously changing the size of each regionand said regions in succession as the scanning of said field proceedsthroughout the scanning period to change the amount of light suppliedfrom varying portions thereof to thereby vary said electromotive force.

16. The method of electro-optically scanning a non-uniform picture fieldwhich comprises progressively continuously varying the size of theregion from which light is utilized by moving a boundary thereof, andcontinuously utilizing the light from said region as the scanningproceeds throughout the scanning period to control the production of anelectromotive force which varies in accordance with the light tonevalues of said field at said boundary.

17. The method of electro-optically scanning a non-uniform picture fieldin elemental strips which comprises progressively continuously varyingthe size of the region within a strip from which light is utilized, saidvariation being produced by changing the position of a boundary of saidregion with respect to the field, repeating this process for successiveelemental strips of the field, and utilizing the light from the field atsuch instant as the scanning proceeds during the complete scanningperiod to control the production of an electromotive force which variesin accordance with the light tone values of said field at said boundary.

18. The method of electro-optically scanning a non-uniform picture fieldin elemental strips which comprises progressively continuously varyingthe size of the region within a strip from which light is utilized, saidvariation being produced by changing the position of a boundary of saidregion with respect to the field, repeating this process for successiveelemental strips of the field, and utilizing the light from said fieldat eachinstant as the scanning proceeds throughout the complete scanningperiod to set up a variable electromotive force.

19. Electro optical apparatus means for scanning a picture field alongan elemental path of very great length compared with its width byprogressively continuously varying the portion of the path from whichlight is utilized as the scanning proceeds throughout the completescanning period, and means for utilizing the light from the path to setup a variable electromotive force.

20. Electro optical apparatus comprising means for scanning anon-uniform picture field along an elemental path of very great lengthcompared with its width including light sensitive means and means forcausing said light sensitive means to receive light from a longitudinalportion of said path of progressively continuous- 13 varying length asthe scanning proceeds throughout the complete scanning period to controlthe production of an electromotive force, and means for deriving fromsaid electromotive force a second electromotive force which va-' ries inaccordance with the non-uniform characteristics of said field along saidpath.

21. Electro-optical apparatus comprising means for optically scanning anon uniform picture field along a path of uniform width by restrictingthe useful light to a longitudinal section of said path of continuouslyprogressively comprising out the complete scanning period, and lightsensitive electric means upon which said useful light impinges to set upan electromotive force having a component representative of thenon-uniform characteristics of said field along said path.

BENJAMIN F. LOFGREN.

